1. Field of the Invention
The present invention relates generally to lithographic projection apparatus and more specifically to lithographic projection apparatus including contamination control structures.
2. Summary of the Related Art
In general, lithographic apparatus include an illumination system for providing a projection beam of radiation, a support structure for supporting patterning means, the patterning means serving to impart the projection beam with a pattern in its cross-section, a substrate table for holding a substrate, a projection system for projecting the patterned beam onto a target portion of the substrate, a dust-tight storage container defining a storage space for containing patterning means, wherein the storage container is arranged to be coupled with a transfer container for exchanging patterning means through a closeable passage between the transfer container and the storage container.
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning means, such as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., comprising part of, one or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
If a new or different pattern has to be imaged on a substrate or wafer then the lithographic apparatus has to be provided with appropriate corresponding patterning structure. Preferably, the patterning structures have to be transferred from a station were the patterning structures are stored and/or manufactured to the lithographic apparatus such that it is delivered to the latter in an essential clean (dust-free) status. For this transfer use is made of transfer containers which enclose the patterning means such that it is stored dust-free.
It is an object of the present invention to provide a system of a lithographic apparatus, patterning structures and a transfer container for such patterning structures, which system is suited for a wide range of applications including for example for projection of Extreme UltraViolet radiation (EUV) on a substrate. Using EUV radiation poses extra requirements on the system as a consequence of specific properties of EUV radiation (note for example that EUV radiation is absorbed in air).
A solution known in the art for providing an EUV projection system (for example see U.S. Pat. No. 5,730,573) is to provide a transfer container which can be placed in a transfer position against the lithographic apparatus, wherein the transfer container forms part of an outer wall of a vacuum chamber of the lithographic apparatus. However, a disadvantage of this solution is that the transfer container has to be designed and arranged such that it has a vacuum compatible construction (being able to withstand relative large pressure differences). This means that no conventional transfer containers can be used with this system. Moreover, if the used transfer container has a vacuum malfunction, the said vacuum chamber of the lithographic apparatus cannot be brought in a vacuum state.
Another solution in the art for providing an EUV compatible system (for example, see U.S. Pat. No. 6,281,510) is to move a dust-tight but non-vacuum compatible transfer container completely in an unload position in a vacuum chamber of the lithographic apparatus, subsequently to pump the vacuum chamber vacuum, after which the patterning means is brought into a vacuum illumination position. A disadvantage of this solution is that it is difficult and time consuming to bring the transfer container completely in an unload position in the vacuum chamber while guaranteeing an accurate placement of the transfer container. Furthermore, bringing the complete transfer container in the vacuum chamber brings the risk of the vacuum chamber to become contaminated with dust particles, while cleaning the vacuum chamber is an awkward job and a source of expensive maintenance.